1. Field of the Invention
The present invention relates to apparatus for controlling the bending of a pipeline. In particular, the present invention is a bending restrictor assembly that serves to limit the bending of a pipeline. Additionally, the present invention relates to bending restrictor assemblies that are used to produce control bending of the pipeline beyond elastic limits. The present invention also relates to bending restrictor assemblies which limit the amount of bending that can occur in the pipeline during the laying of the pipeline or during the maintaining of the pipeline at the seafloor.
2. Description of Related Art including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Subsea pipelines are typically assembled one segment at a time aboard a pipeline-laying vessel. As each segment is added, the vessel moves forward and the pipeline follows a descending path to the sea floor. The suspended pipe span between the vessel stern and the sea floor is typically supported partly by a ramp attached to the vessel and axial tension is applied to the pipe which maintains the pipeline steel within elastic boundaries until reaching on the seabed.
The steel pipelines that are laid on the bottom of the sea cannot be pre-formed or pre-adapted to the contour of the sea floor. This is because of the above-identified laying and installation procedure.
There may be tolerated a certain degree of unevenness over which the pipeline is capable of spanning or bending, provided that the specific load does not produce excessively high stresses in the pipeline steel or cause vortex-induced vibrations. If stresses exceed allowable limits, the pipeline could be deformed permanently, either by buckling or cold bending, or both to an unacceptable configuration. Should cold bending occur through yielding of the steel in the pipeline, it could propagate uncontrollably. Requirements set by classification societies for construction and operation of offshore pipelines permit a certain degree of cold bending beyond elastic limits provided that it takes place under controlled conditions. Parameters for such controlled conditions entail that a pipeline may be cold bent to a minimum radius less than what is allowed for uncontrolled bending.
Pipelines that are laid on an uneven sea floor are subjected to free spanning because of the rigidity of the pipeline. Specifications used for submarine pipeline installation permits plastic deformation as long as positive measures are taken to ensure that excessive bending is prevented. By allowing plastic deformation, it is possible to reduce to a considerable degree the occurrence of free spanning Bending beyond elastic limits may be achieved by overloading the pipeline by applying external loads.
Submarine pipelines having a diameter of more than twelve inches usually require a weight coating to achieve negative buoyancy. This is necessary if the pipeline is to be submerged and also maintain a stable state with respect to the sea current. Plastic deformation of a pipeline having a weight coating of concrete will cause the concrete to crack and break loose.
In the past, various patents and publications have issued relating to the controlling of the bending of a pipeline. For example, U.S. Pat. No. 5,192,166, issued to the present inventor, describes a method for controlled bending of a pipeline during the laying thereof in the sea. This method utilizes bend controlling/stopping means which are mounted on the pipeline and interact with the pipeline. To achieve cold bending under controlled conditions, the pipeline is weight-loaded internally at the selected bending zone. The weight-loading may be achieved by means of a flexible string of weight elements and/or by introducing into the pipe a suitable heavy, readily flowable weight mass, for example, drilling fluid or water.
U.S. Pat. No. 5,403,121, issued on Apr. 4, 1995 to Lanan, describes a method for accommodating thermal expansion of a buried subsea pipeline. This method includes the steps of providing a pipeline which bends in alternating essentially opposed directions. The angles of the bends and the distance between the bends are sufficiently small so that the pipeline is not plastically deformed when resting on the seabed. The number and angles of the bends are sufficiently large to prevent upheaval buckling. The bend angles and distance between the bends is small enough that the pipeline can be passed through a tensioning machine and ramp of a pipeline-laying vessel. The pipeline can then be installed on the sea floor.
U.S. Pat. No. 1,677,077, issued on Jul. 10, 1928 to D. D. Fortune, describes a hose protector in which a flexible sheath is connected to a collar. The sheath comprises a plurality of sections pivotally connected together. Each section is formed of a plurality of rings. Straps connect the rings together. An end of each strap projects beyond a ring and is pivotally connected to a ring of an adjacent section. The collars form a plurality of section pivotally connected together. This method is applicable for preventing kinking of a flexible hose,
U.S. Patent Publication No. 2010/0329792, published on Dec. 30, 2010 to the present inventor, describes a controlled bending of a pipeline by an external force. A bending collar assembly is attached to a selected bending zone of the pipeline so as to limit the control bending of the pipeline to a predetermined resulting bending configuration. External force is then applied on the bending collar assembly so as to bend the pipeline to the resulting bending configuration in cooperation with the bending collar assembly and the sea floor. The external force can be exerted from one or more weights placed on top of the bending collar assembly.
U.S. Pat. No. 8,562,255, issued Oct. 22, 2013 to the present inventor, describes a bending restrictor assembly for use with a pipeline section. The bending restrictor assembly has a sleeve affixed to the pipeline section, an outer collar slidably positioned relative to an over the sleeve, and it inner collar slidably positioned relative to an interior of the outer collar. The inner collar is in spaced longitudinal relation to an end of the sleeve. The inner and outer collars are slidable relative to a bending of the pipeline section. A series of holes and keyways are formed in the inner and outer collars. Pins are inserted into corresponding holes and keyways so as to correspond to a limit of the bending radius of the pipeline section.
It is an object of the present invention to provide a bending restrictor assembly that allows cold bending to be achieved at the seabed during pipeline installation operations.
It is another object the present invention to provide a bending restrictor assembly which allows for a pipeline to bend within predetermined limits.
It is another object of the present invention to provide a bending restrictor assembly which, when applied, can alleviate seabed preparation and post-installation corrections.
It is another object of the present invention to provide a bending restrictor assembly which can be installed on the pipeline section before being added to the pipeline as part of a final installation.
It is another object of the present invention to provide a bending restrictor assembly which can result in significant cost savings.
It is still further object of the present invention to provide a bending restrictor assembly which provides for the easy installation of smooth transition areas between the pipeline and the bending restrictor assembly.
It is still another object of the present invention provide a bending restrictor assembly which enhances the strength of the pipeline in the area of the transition between the pipeline of the bending restrictor assembly.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.